Editing Lake Tahoe (section)

==Environmental issues==

===Water quality===
[[File:lake tahoe storm drain el dorado beach 2.jpg|thumb|An example of road runoff with fine sediment, failing to reach its sluice, at El Dorado Beach. This [[storm drain]] was removed during construction of a new beach, called Lakeview Commons, opened in mid-2012.]]
{{Image frame |caption={{center|Average Lake Tahoe [[water clarity|Clarity]]{{snd}}As Measured by [[Secchi disk|Secchi Depth]].<ref name="UC Davis">{{cite web|title=Average Lake Tahoe Secchi Depth|url=https://tahoe.ucdavis.edu/sites/g/files/dgvnsk4286/files/inline-files/Secchi_Averages_2023_final.pdf|website=Tahoe Environmental Research Center (TERC)|publisher=University of California, Davis|access-date=August 2, 2024}}</ref>}}|content=
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|x=1968,1969,1970,1971,1972,1973,1974,1975,1976,1977,1978,1979,1980,1981,1982,1983,1984,1985,1986,1987,1988,1989,1990,1991,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001,2002,2003,2004,2005,2006,2007,2008,2009,2010,2011,2012,2013,2014,2015,2016,2017,2018,2019,2020,2021,2022,2023
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|y2=109.6,119.1,99.4,109.9,85.6,96.8,97.4,94.5,90.6,91.2,87.6,95.1,90.9,81.7,90.6,95.1,72.2,89.6,88.3,76.1,77.4,87.6,84.6,70.9,72.5,84.6,71.5,75.1,88.3,65.6,76.1,81,70.5,77.8,78.4,70.9,83.3,80.4,76.8,82.3,85.3,81.4,72.8,85,88.3,77.8,79.1,71.5,83.3,78.7,73.5,81.0,64.0,71.9,72.2,91.9
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}}
}}
Despite land-use planning and export of treated [[sewage]] effluent from the basin, the lake is becoming increasingly [[eutrophic]] (having an excessive richness of nutrients), with primary productivity increasing by more than 5% annually, and clarity decreasing at an average rate of {{convert|0.25|m|ft|order=flip}} per year.<ref>{{cite web|author=Lahontan Regional Water Quality Board|title=Lake Tahoe Basin Characterization & Assessment of Exemplary Programs for Water Quality Crediting and Trading Feasibility Analysis |url=http://www.enviroincentives.com/Tahoe%20Crediting_Trading%20Characterization%20and%20Cases%20draft%20v1.1.pdf |archive-url=https://web.archive.org/web/20120426023041/http://www.enviroincentives.com/Tahoe%20Crediting_Trading%20Characterization%20and%20Cases%20draft%20v1.1.pdf|archive-date=April 26, 2012|website=Water Quality Crediting and Trading Feasibility Study|publisher=Kieser and Associates|access-date=December 6, 2011 |url-status=dead}}</ref>  Until the early 1980s, nutrient-limitation studies showed that primary productivity in the lake was nitrogen-limited. Now, after a half-century of accelerated nitrogen input (much of it from direct atmospheric deposition), the lake is phosphorus limited. Theodore Swift et al.,<ref name=Swift>{{cite journal|first1=Theodore J|last1=Swift|first2=Joaquim|last2=Perez-Losada|first3=S. Geoffrey|last3=Schladow|first4=John E|last4=Reuter|first5=Alan D|last5=Jassby|first6=Charles R|last6=Goldman|title=Water clarity modeling in Lake Tahoe: Linking suspended matter characteristics to Secchi depth|journal=Aquat. Sci.|volume=68|year=2006|issue=1 |pages=1–15|doi=10.1007/s00027-005-0798-x|bibcode=2006AqSci..68....1S |s2cid=37395769}}</ref> concluded that "suspended inorganic sediments and phytoplanktonic algae both contribute significantly to the reduction in clarity, and that suspended particulate matter, rather than dissolved organic matter, are the dominant causes of clarity loss." The largest source of fine sediment particles to Lake Tahoe is urban stormwater runoff, constituting 72 percent of the total fine sediment particle load.<ref>{{cite web|title=Lake Tahoe Total Maximum Daily Load Report|url=http://www.waterboards.ca.gov/lahontan/water_issues/programs/tmdl/lake_tahoe/docs/tmdl_rpt_nov2010.pdf|publisher=California Regional Water Quality Control Board, Lahontan Region|year=2010}}</ref> Recent research has shown that the urban uplands also provide the largest opportunity to reduce fine sediment particle and phosphorus contributions to the lake. Historic clarity of approximately {{convert|30|m|ft|order=flip}} can be achieved with total reduction of approximately 75 percent from urban sources.<ref name=sahoo>{{cite journal|last=Sahoo |first=G. B. |author2=Schladow, S. G. |author3=Reuter, J. E. |journal=Water Resources Research |year=2010 |volume=46 |doi=10.1029/2009WR008447 |url=http://www.agu.org/pubs/crossref/2010/2009WR008447.shtml |title=Effect of sediment and nutrient loading on Lake Tahoe optical conditions and restoration opportunities using a newly developed lake clarity model |issue=10 |pages=n/a |bibcode=2010WRR....4610505S |s2cid=140172942 |url-status=dead |archive-url=https://web.archive.org/web/20120120034206/http://www.agu.org/pubs/crossref/2010/2009WR008447.shtml |archive-date=January 20, 2012 }}</ref>

Historically, the clarity of Lake Tahoe continued to decrease through 2010, when the average [[Secchi depth]], {{convert|64.4|ft|m}}, was the second lowest ever recorded (the lowest was {{convert|64.1|ft|m}} in 1997). This represented a decrease of {{convert|3.7|ft|m}} from the previous year.<ref name="sotl2011">{{cite web|url=http://terc.ucdavis.edu/stateofthelake/StateOfTheLake2011.pdf|title=Tahoe: State of the Lake Report|year=2011 |publisher=UC Davis Tahoe Environmental Research Center |archive-url=https://web.archive.org/web/20111208070952/http://terc.ucdavis.edu/stateofthelake/StateOfTheLake2011.pdf |archive-date=December 8, 2011 |url-status=dead}}</ref> However, the lake's clarity increased from 2011 to 2014, improving by nearly 20 percent.<ref>{{cite web|url=http://www.sacbee.com/2013/02/28/5224182/lake-tahoes-clarity-shows-gains.html|archive-url=https://web.archive.org/web/20130306111953/http://www.sacbee.com/2013/02/28/5224182/lake-tahoes-clarity-shows-gains.html|archive-date=March 6, 2013|title=Lake Tahoe's clarity shows gains for a second year}}</ref><ref>{{Cite web|url=https://www.rgj.com/story/tech/environment/2015/04/07/drought-helps-boost-lake-tahoes-clarity/25416091/|title=Drought helps boost Lake Tahoe's clarity|first=Jeff|last=DeLong|website=Reno Gazette Journal|access-date=February 15, 2022}}</ref>

A water quality study by the Lahontan Water Quality Control Board and the Nevada Division of Environmental Protection<ref>{{cite web|archive-url=https://web.archive.org/web/20150924063247/http://ndep.nv.gov/bwqp/file/LTTMDL_NDEP_Final.PDF|archive-date=September 24, 2015|url=http://ndep.nv.gov/bwqp/file/LTTMDL_NDEP_Final.PDF|title=Lake Tahoe Total Maximum Daily Load for Fine Sediment Particles, Nitrogen and Phosphorus|first=Colleen|last=Cripps|publisher=Nevada Department of Conservations and Natural Resources|date=August 3, 2011}}</ref> determined the largest source of fine [[sediment]] particles: 71 percent is developed area (urban) erosion and run-off, much of it associated with transportation infrastructure and services.<ref>{{cite web|url=http://ndep.nv.gov/bwqp/tahoe3.htm|archive-url=https://web.archive.org/web/20110916102925/http://ndep.nv.gov/bwqp/tahoe3.htm|archive-date=September 16, 2011|title=Final EPA Approved Lake Tahoe TMDL Report|publisher=Nevada Bureau of Water Quality Planning}}</ref>

Lake Tahoe is a tributary watershed drainage element within the Truckee River Basin, and its sole outlet is the Truckee River, which continues on to discharge to Pyramid Lake. Because of the sensitivity of Truckee River water quality (involving two protected species, the [[cui-ui]]<ref>{{cite iucn |author=NatureServe |date=2014 |title=''Chasmistes cujus'' |volume=2014 |page=e.T4586A3003395 |doi=10.2305/IUCN.UK.2014-3.RLTS.T4586A3003395.en |access-date=November 11, 2021}} Listed as Critically Endangered (CR B1+2b v2.3)</ref> [[Catostomidae|sucker fish]] and the [[Lahontan cutthroat trout]]), this drainage basin has been studied extensively. The primary investigations were stimulated by the [[United States Environmental Protection Agency|U.S. Environmental Protection Agency]], which funded the development of the [[DSSAM]] model to [[hydrology transport model|analyze water quality]] below Lake Tahoe.

Lake Tahoe never freezes.<ref>{{cite web |url=http://www.skiheavenly.com/lake-tahoe/tahoe-town-facts.aspx |title=Lake Tahoe Facts |access-date=October 3, 2010 |publisher=[[Heavenly Mountain Resort]] |archive-url=https://web.archive.org/web/20110106193151/http://www.skiheavenly.com/lake-tahoe/tahoe-town-facts.aspx |archive-date=January 6, 2011 |url-status=dead }}</ref> Since 1970, it has mixed to a depth of at least {{convert|1300|ft|abbr=on}} a total of six or seven times. Dissolved oxygen is relatively high from top to bottom. Analysis of the temperature records in Lake Tahoe has shown that the lake warmed (between 1969 and 2002) at an average rate of {{cvt|0.015|C-change|order=flip|}} per year. The warming is caused primarily by increasing air temperatures, and secondarily by increasing downward long-wave radiation. The warming trend is reducing the frequency of deep mixing in the lake and may have important effects on [[water clarity]] and nutrient cycling.<ref>{{Cite book |date=2022 |title=Scientific Investigations Report |chapter=Seasonal and long-term clarity trend assessment of Lake Tahoe, California–Nevada |language=en |doi=10.3133/sir20225070|last1=Naranjo |first1=Ramon C. |last2=Work |first2=Paul |last3=Heyvaert |first3=Alan |last4=Schladow |first4=Geoffrey |last5=Cortes |first5=Alicia |last6=Watanabe |first6=Shohei |last7=Tanaka |first7=Lidia |last8=Elci |first8=Sebnem }}</ref>

{{See also|List of Lake Tahoe inflow streams}}

===Ecosystem changes===
Since the 1960s, the Lake's food web and [[zooplankton]] populations have undergone major changes. In 1963–65, [[Mysida|opossum shrimp]] (''[[Mysis diluviana]]'') were introduced to enhance the food supply for the introduced [[Kokanee salmon]] (''Oncorhynchus nerka'').<ref>{{Cite news|url=https://www.latimes.com/environment/story/2019-09-06/lake-tahoe-clarity-shrimp-pollution|title=Will Lake Tahoe's invasive shrimp become the next mass-market health supplement?|date=September 7, 2019|newspaper=[[Los Angeles Times]]|first=Louis |last=Sahagun|language=en-US|access-date=September 8, 2019}}</ref> The shrimp began feeding on the lake's [[cladoceran]]s (''[[Daphnia]]'' and ''[[Bosmina]]''), and their populations virtually disappeared by 1971.<ref>{{cite journal|author=Goldman, C.R.|author2=M.D. Morgan|author3=S.T. Threlkeld|author4=N. Angeli|title=A Population Dynamics Analysis of the Cladoceran Disappearance from Lake Tahoe, California-Nevada|journal=Limnology and Oceanography|volume=24|pages=289–97|year=1979|issue=2|doi=10.4319/lo.1979.24.2.0289|citeseerx=10.1.1.556.6018|bibcode=1979LimOc..24..289G}}</ref> The shrimp provide a food resource for salmon and [[trout]], but also compete with juvenile fish for zooplankton. Since the 1970s, the cladoceran populations have somewhat recovered, but not to former levels. Since 2006, [[goldfish]] have been observed in the lake, where they have grown to "giant size". An [[invasive species]], they may have descended from former pets which owners dumped, or when used as fishing bait.<ref>Laila Kearney. Goldfish influx threatens to cloud pristine Lake Tahoe waters. Reuters February 22, 2013.</ref>

The Lake Tahoe area is prone to wildfires, particularly the [[South Lake Tahoe]] region. The areas around are heavily forested, with four more times as much understory trees than in recent years. They are some of the most flammable types of trees.<ref>{{cite news |last1=Cart |first1=Julie |title='It will not be survivable': Lake Tahoe could be a deathtrap during major wildfires |url=https://thenevadaindependent.com/article/it-will-not-be-survivable-lake-tahoe-could-be-a-deathtrap-during-major-wildfires |access-date=April 15, 2025 |work=The Nevada Independent |date=March 26, 2025}}</ref> In June 2007, the [[Angora Fire]] burned approximately {{convert|3100|acre|abbr=on}} throughout the South Lake Tahoe area. While the impact of ash on the lake's ecosystem is predicted to be minimal, the impact of potential future erosion is not yet known.<ref>{{cite news|title=Raging Tahoe Fire's Roots: 150 Years of Mismanagement|author=Carl T. Hall|newspaper=San Francisco Chronicle|date=June 26, 2007|page=A-1}}</ref>

===Environmental protection===
[[File:Emerald Bay.jpg|thumb|left|Emerald Bay, Lake Tahoe]]
[[File:Secret Beach - Lake Tahoe East Shore.jpg|thumb|left|Secret Beach on Lake Tahoe's Nevada side]]
Construction activities have resulted in a clouding of the lake's blue waters. Currently, the Tahoe Regional Planning Agency is regulating construction along the shoreline<ref>{{cite web|url=http://www.trpa.org/default.aspx?tabindex=1&tabid=40 |archive-url=https://web.archive.org/web/20110716131956/http://www.trpa.org/default.aspx?tabindex=1&tabid=40 |archive-date=July 16, 2011 |title=Construction Monitoring |publisher=Tahoe Regional Planning Agency |url-status=dead }}</ref> (and has won two [[Tahoe-Sierra Preservation Council, Inc. v. Tahoe Regional Planning Agency|Federal Supreme Court battles over recent decisions]]).<ref name="535 U. S. 302">{{cite court |litigants=Tahoe-Sierra Preservation Council, Inc. v. Tahoe Regional Planning Agency |vol=535|reporter=U.S.|opinion=302 |court=[[Supreme Court of the United States]] |date=2002 |url=https://www.law.cornell.edu/supct/html/00-1167.ZS.html |access-date=July 13, 2018 }}</ref> These regulations are unpopular with many residents, especially those in the Tahoe Lakefront Homeowners Association.<ref>{{cite web|title=About TLOA|url=http://www.tloa.net/pages/tloa-home/about-tloa.php|archive-url=https://web.archive.org/web/20120426023044/http://www.tloa.net/pages/tloa-home/about-tloa.php|archive-date=April 26, 2012|publisher=Tahoe Lakefront Homeowners Association|access-date=December 6, 2011}}</ref>

The League to Save Lake Tahoe (Keep Tahoe Blue) has been an environmental watchdog in the Lake Tahoe Basin for 50 years.<ref name=bluehistory/> Founded when a proposal to build a four-lane highway around the lake—with a bridge over the entrance to Emerald Bay—was proposed in 1957, the League has opposed many development projects in the area, which it alleges were environmentally harmful. The League embraces responsible and diversified use of the Lake's resources while protecting and restoring its natural attributes.<ref name=bluehistory>{{cite web |url=http://www.keeptahoeblue.org/about-us/history |title=History of The League to Save Lake Tahoe |publisher=Keep Tahoe Blue |access-date=September 25, 2008}}</ref>

Since 1980, the Lake Tahoe Interagency Monitoring Program (LTIMP) has been measuring stream discharge and concentrations of nutrients and sediment in up to 10 tributary streams in the Lake Tahoe Basin, California-Nevada. The objectives of the LTIMP are to acquire and disseminate the water quality information necessary to support science-based environmental planning and decision making in the basin. The LTIMP is a cooperative program with support from 12 federal and state agencies with interests in the Tahoe Basin. This data set, together with more recently acquired data on [[urban runoff]] water quality, is being used by the Lahontan Regional Water Quality Control Board to develop a program (mandated by the Clean Water Act) to limit the flux of nutrients and fine sediment to the Lake.

[[Microplastics]] were found for the first time in 2019 by the [[Desert Research Institute]]. This pollution in the water could be local or from locations around the world as particles from discarded plastic products can be transported long distances through the atmosphere by wind, rain and falling snow.<ref>{{Cite news|url=https://www.latimes.com/environment/story/2019-08-26/lake-tahoe-microplastic-pollution-detected|title=Microplastics are found in Lake Tahoe's waters for first time ever|last=Sahagun|first=Louis|date=August 26, 2019|newspaper=[[Los Angeles Times]]|language=en-US|access-date=August 27, 2019}}</ref> In 2023, updated measurements of microplastics in the lake revealed that Lake Tahoe contained some of the highest microplastic pollution concentrations found among 38 lakes and reservoirs measured.<ref>{{Cite journal |last1=Nava |first1=Veronica |last2=Chandra |first2=Sudeep |last3=Aherne |first3=Julian |last4=Alfonso |first4=María B. |last5=Antão-Geraldes |first5=Ana M. |last6=Attermeyer |first6=Katrin |last7=Bao |first7=Roberto |last8=Bartrons |first8=Mireia |last9=Berger |first9=Stella A. |last10=Biernaczyk |first10=Marcin |last11=Bissen |first11=Raphael |last12=Brookes |first12=Justin D. |last13=Brown |first13=David |last14=Cañedo-Argüelles |first14=Miguel |last15=Canle |first15=Moisés |date=July 2023 |title=Plastic debris in lakes and reservoirs |url=https://www.nature.com/articles/s41586-023-06168-4 |journal=Nature |language=en |volume=619 |issue=7969 |pages=317–322 |doi=10.1038/s41586-023-06168-4 |pmid=37438590 |bibcode=2023Natur.619..317N |issn=1476-4687|hdl=10198/19283 |s2cid=259835082 |hdl-access=free }}</ref><ref>{{Cite web |last=Spencer |first=Cari |date=2023-07-14 |title=Lake Tahoe has higher concentration of microplastics than ocean trash heap |url=https://www.latimes.com/california/story/2023-07-14/lake-tahoe-troubling-concentration-microplastics |access-date=2023-07-29 |website=Los Angeles Times |language=en-US}}</ref><ref>{{Cite news |last=Thomas |first=Gregory |date=12 July 2023 |title=Lake Tahoe has alarmingly high concentrations of microplastics, study finds |work=The San Francisco Chronicle |url=https://www.sfchronicle.com/tahoe/article/plastic-pollution-18189271.php}}</ref> Restoring the Lake Depths Foundation uses a BlueROV2 to survey the bottom of Lake Tahoe in an organized grid pattern to remove microplastics and trash.<ref>{{Cite web |last=Dailey |first=Scott |date=2022-08-23 |title=Peninsula residents use high-tech 'gripper' to snatch junk from bottom of Lake Tahoe |url=https://climaterwc.com/2022/08/23/peninsula-residents-use-high-tech-gripper-to-snatch-junk-from-bottom-of-lake-tahoe/ |access-date=2024-01-18 |website=Climate Online |language=en-US}}</ref>

The UC Davis [[Tahoe Environmental Research Center]] is dedicated to research, education and public outreach, and to providing objective scientific information for restoration and sustainable use of the Lake Tahoe Basin.<ref name=terc>{{Cite web|url=https://tahoe.ucdavis.edu/|title=Tahoe Environmental Research Center|website=Tahoe.ucdavis.edu|access-date=February 15, 2022}}</ref> Each year, it produces a "State of the Lake" report, assessing changes such as lake clarity, nutrients and particles, or meteorology around the lake.
[[File:Lake Tahoe Near Cave Rock.jpg|thumb|A view from the east shore of Lake Tahoe]]